I've been trying some diptychs lately -- two adjacent, or nearly adjacent, views, to be hung together either one above the other or side by side.
What worked well the other day was putting down a thin wash of OMS (odorless mineral spirits) and pigment a short while before painting. I tried to achieve what I thought of as the color of "parchment": a little cadmium yellow light + cad yellow medium + cad red light to make a bright yellow-orange, then some black (ultra blue+ alizarin + cad yellow medium) to take it towards golden brown...when diluted with spirits against the white of the ground, voila, "parchment." I put down that wash, then went for a walk, and by the time I started to paint, the surface was very soft and smooth -- super-easy to apply paint to: it just glided on. Very nice for getting down a quick layer, and little fighting against small white speckles (the ground showing through).
Also, it worked to mix a LOT of paint up front -- something I often don't do. I tend to mix a few general colors, then add pure color as I go, but I mixed a few more specific colors than usual, and having more paint on hand helped me move more quickly. I tried to stay in a sort of half-thinking state of mind -- the same as I do for painting -- to create the colors, and as usual, that worked better than thinking. It seems like my gut is much better at shorthand than my brain, which is better at detail. And painting is largely about shorthand, so that makes sense.
I wonder what painters say to themselves when facing difficult challenges, such as (as I am facing now) coming back to a painting on the second day/session. "Don't think"? As always, that might be a good one. And: "Keep moving" around the painting -- don't get stuck in one spot.